In recent years, it has become apparent that large reserves of hydrocarbons are to be found in what are referred to as “unconventional” oil and gas bearing geologic layers. These unconventional layers, which include rock types such as shales, are typically not highly permeable, and therefore present formidable obstacles to production. The most common technique in use today that permits commercial production of natural gas and oil from such layers is hydraulic fracturing, also referred to as “fracing” or “fracking”. This technique can be also be applied to older wells drilled through conventional hydrocarbon-bearing layers to increase the proportion of hydrocarbons that can be extracted from them, thus prolonging well life.
The progress of a fracturing operation must be monitored carefully. Well fracturing is expensive, and the fracturing process is done only when the expected resulting increase in production is significant. The high pressures associated with fracturing result in new fractures that may follow existing faults and fractures, which can result in an uneven or unpredictable fracture zone. Fracturing fluid may also begin following an existing fault or fracture zone and then propagate beyond the intended fracture zone. If the induced fracturing grows out of the target horizon it can contact nearby water bearing layers so that the well is ruined by water influx. If the induced fracturing grows out of zone the well may be ruined both because the target horizon is not stimulated or because the produced hydrocarbons leak off.
Knowledge of the actual induced fracture size, location, shape etc. provides valuable data for designing better fracturing operations and provides for better reservoir simulations. Care must also be taken not to interfere with existing oil or gas production wells in the area. For these and other reasons, it is important that the that the operator planning the fracturing operation be able to accurately predict where the injected fluid will go.
Among other things, what is required are means and methods for determining the natural permeability and fracturing of geologic layers and zones of potential fluid loss before hydraulic fracturing is undertaken to plan where hydraulic fracturing should be performed, and in which zones hydraulic fracturing should be avoided.